Process for the production of alpha-alumina from aluminum fluoride



March 27, 1962 H. WOREL ETA PROCESS FOR THE PRODUCTION OF ALUMINA FROMALUMINUM FLUORIDE Filed May 2, 1958 TEMPERATURE HUMIDITY ATTORNEY 5 3027 231 enemies non ram reionucrron or tit-ALA FRQM ALUMENUM FLUDREDEHeinrieh Worel, Vienna, and Karl Torirar, Graz, Austria,

assignors to Peter Spence 8; uns Limited, Widnes, England, a Britishcompany, and Deutsche Golduntl Silber-Scheideanstait vormals Roessier,Frankfurt, German, a German joint-stock company Filed May 2, 1958, Ser.No. 732,433 Claims priority, appiication Great Britain May 11, 1957 '7Claims. (Cl. 23-442) This invention is concerned with a process forproducing corundum (CC-Ellll'l'lll'lil).

Aluminium oxide as such or as hydrous alumina finds application in thechemical industry, pre-eminently in oil working and refining, as acatalyst or catalyst support. F or catalytic purposes, it is importantnot only to have the material in the purest possible state, but withregard to catalytic activity, in the most definite and reproducible formpossible. Such a requirement is not confined only to the shape and sizeof the particles in which the catalyst or support is to be used, butapplies also to its modification, through a correct choice of which aknown directing of the catalytic process is made possible or improved.Consequently it is to be recommended, in the production of pure aluminumoxide, that the form and composition of the product with regard to theresulting modification of the oxide or hydroxide. be not left more orless to chance, but through definite production conditions desired endproducts of greatest possible uniformity be obtained reproducibly.

An object of the present invention is to produce a method of preparingcorundum (ix-alumina) at comparatively low temperatures.

In one form of the invention the aluminium fluoride is heated to atemperature within the range 700975 C. in air, oxygen or an oxygencontaining gaseous mixture having a humidity lying within the range 10'to 10 mg. H O per litre.

In one preferred form of the invention, the aluminium fluoride is heatedto a temperature within the range 700- 900 C. in a stream of air, oxygenor an oxygen containing gaseous mixture having a rate of flow of 12litres per hour and a humidity lying within the range 10- to 3 mg. H Oper litre.

In a specific form of the invention, the aluminium fluoride is heated ata temperature of 700 C. in a stream of air, oxygen or an oxygencontaining gaseous mixture having a rate of flow of 12 litres per hourand a humidity of 0.5 mg H O per litre.

The invention will now be more particularly described by reference tothe following example and to the graph illustrated in the drawing.

EXAMPLE The composition of the AIR; used had the following constitution:

A1 as A11 30-31%.

SiO Max. 0.2%.

Fe O Max. 0.1%.

H Max. 0.5%.

Al (S0 Max. 1%.

Na Max. 0.2% (ca. 0.4% NaF). A1 0 Max. ca. 2.5 (residue).

The series of experiments were carried out 1'11 an electrical resistanceoven.

Apart from temperature and humidity of the gases, the rate of flow ofthe gas, and the type of gas (compressed air, laboratory air and oxygen)were varied. The gas 3,027,231 Patented Mar. 27, 1962 humidity wasvaried from 10- to 10 mg. H O per litre.

The heating series was carried out as follows: The AlF was put into aDegussite boat, i.e. a porcelain elongated crucible, and this taken to450 C. in the Pythag 5 oras tube. Every 12 hours a small part of thesample was taken out for Xray examination and the temperature raised 50C. Rate of gas flow 12. or 25 litres per hour.

As will be evident from the graph of the drawing, at

humidities in the range 10" to 10* mg. H O per litre of gas, there isdirect conversion of AlF to oc-Al O at 950l000 C. At 10" mg, theconversion temperature drops to 850 C., and at 10" to 750 C.

When air with a humidity of 0.5 mg. H O per litre is used, the AlF goesto (It-A1203 at 700 C., the lowest conversion temperature observed.

If the humidity is raised to 3 mg. R 0 per litre, there appears aproduct which exhibits an X-ray powder diagram of 'y-alumina withintensity displacement of the 20 lines and some additional lines betweenAlF and the a-Al O phase. This 'y-like region is, at 3 mg. H O perlitre, already fairly large (550900 C.) and broadens with increasedmoisture content of the gas; e.g. at 11 mg. H O per litre (correspondingto ca. laboratory air) from 500 to 950 C. With pure Water vapour this'y-like product is formed at 450 C. and only goes to aat 1000 C.

Thus it will be appreciated that a humidity of 0.5' mg. H O per litre isof particular importance; detailed results are as follows.

Table I Type of gas: Air from a compressed air supply, 12 litres peroriiiii s'rze AlFa: 120-2s0 mg.

Humidity: 0.5 mg. H2O per litre produced by HZSOA, d.:168).

Temp. Time Product 12 AlFa.

24 AlFa.

36 AlFa.

48 AlFa.

6O AlFs.

72 d-Alsos (preponderant). 84 aAlzOa (sharp). 96 wAlgOa (sharp). 108ouAlgOs (sharp). 120 Ct-AlflOB (sharp). 132 ctr-A1203 (sharp). 144cit-A1203 (sharp).

Table II Type of gas: Air from a compressed air supply, 12 litres perhour. 0 Humidity 0.5 mg. H2O per litre. 6 Grain size of Am: 120-2s0 mg.

Temperature: 700 C.

Time Product AlF AlFg.

AlFa trace a-AlzOa. All s trace a-Al203. Partially a-Alzoa.

Predominantly a-Alzoa. 42 hrs zx-AlzOa.

Thus, with a slowly rising temperature (all 12 hrs. in-

crements of 50 C.) one obtains with passage of air at 0.5 mg. H O perlitre the lowest conversion temperature (700 C.) for conversion of AlFto (Jr-A1 0 Lower humidity raises the conversion temperature; withhigher humidity there appears between AIR; and w-A1 O an ever extending'y-like region.

We claim:

1. A process of preparing corundum (or-alumina) comprising heatingaluminium fluoride in a gaseous medium selected from the groupconsisting of air, oxygen and an oxygen containing gaseous mixture, to atemperature Within the range 7001000 C., said gaseous medium having ahumidity lying within the range 10- to 3 mg. H O per litre, the humidityof said gaseous medium at a given temperature within said temperaturerange corresponding to that indicated by the solid line of theaccompanying graph.

2. Aprocess of preparing corundum (ix-alumina) comprising heatingaluminium fluoride to a temperature Within the range 700-975 C. in agaseous medium selected from the group consisting of air, oxygen and anoxygen containing gaseous mixture, said gaseous medium having a humiditylying Within the range 10** to 10 mg. H O per litre, the humidity ofsaid' gaseous medium at a given temperature within saidtemperature rangecorresponding to that indicated by the solid line of the accompanyinggraph.

3. A process of preparing corundum (or-alumina) comprising heatingaluminium fluoride to a temperature within the range 700900 C. in agaseous medium selected from the group consisting of air, oxygen and anoxygen containing gaseous mixture, said gaseous medium having a humiditylying within the range 10 to 3 mg. H O per litre, the humidity of saidgaseous medium at a given temperature Within said temperature rangecorresponding to that indicated by the solid line of the accompanyinggraph.

4. A process of preparing corundum (or-alumina) comprising heatingaluminium fluoride to avtemperature of 700 C. in a gaseous mediumselected from the group consisting of air, oxygen and an oxygencontaining gaseous mixture, said gaseous medium having a humidity of 0.5mg. H O per litre.

5. A process of preparing corundum (or-alumina) comprising heatingaluminium fluoride to a temperature within the range 700900 C. in astream of a gaseous medium selected from the group consisting of air,oxygen and an oxygen containing gaseous mixture, said gaseous mediumhaving a rate of flow of 12 litres per hour and a humidity lying withinthe range 10- to 3 mg. H O per litre, the humidity of said gaseousmedium at a given temperature within said temperature rangecorresponding to that indicated by the solid line of the accompanyinggraph.

6. .A process of preparing corundum (oz-alumina) comprising heatingaluminium fiuoride to a temperature of 700 C. in a stream of a gaseousmedium selected from the group consisting of air, oxygen and an oxygencontaining gaseous mixture, said gaseous medium having a rate of flow of12 litres per hour and a humidity of 0.5 mg. H O per litre.

7. A process of preparing corundum (or-alumina) com prising heatingaluminium fluoride to a temperature of 700 C. in a stream of airobtained from a compressed air supply and having a rate of flow of 12litres per hour and a humidity of 0.5 mg. H O per litre.

References Cited in the file of this patent UNITED STATES PATENTS2,333,948 Muskat Nov. 9, 1943 2,614,028 Schaumann Oct. 14, 19522,833,622 Roberts et al May 6, 1958 FOREIGN PATENTS 165,589 AustraliaOct. 13, 1955 OTHER REFERENCES Mellor: Comprehensive Treatise onInorganic and Theoretical Chemistry, vol. 5, pages 261 and 300 to 302,Longman, Green & Co., New York, 1924.

1. A PROCESS OF PREPARING CORUNDUM (A-ALUMINA) COMPRISING HEATINGALUMINUM FLUORIDE IN A GASEOUS MEDIUM SELECTED FROM THE GROUP CONSISTINGOF AIR, OXYGEN AND AN OXYGEN CONTAINING GASEOUS MIXTURE, TO ATEMPERATURE WITHIN THE RANGE 700-1000*C., SAID GASEOUS MEDIUM HAVING AHUMIDITY LYING WITHIN THE RANGE 10-6 TO 3 MG. H2O PER LITRE, THEHUMIDITY OF SAID GASEOUS MEDIUM AT A GIVEN TEMPERATURE WITHIN SAIDTEMPERATURE RANGE CORRESPONDING TO THAT INDICATED BY THE SOLID LINE OFTHE ACCOMPANYING GRAPH.